Supervisors: Xize Niu (lead, UoS), Sinhue Torres-Valdes (NOC), Alexander Beaton (NOC)
Determining the variation and distribution of chemical species within the oceans is fundamental to understanding the biogeochemical cycles that underpin elemental transport and biological productivity across the globe. Traditionally most chemical parameters (e.g. nitrate, phosphate) are measured by laboratory analysis of discrete water samples. Microfluidic sensors offer an attractive alternative: by taking and analysing samples autonomously in situ, they obviate sampling allowing larger datasets particularly when used in conjunction with autonomous systems. The current state-of-the-art sensors have temporal resolution of minutes due to Taylor dispersion (fluid flow effectively smears chemical composition within the device) making them unsuitable for deployments requiring high frequency measurement – most notably on profiling vehicles (e.g. Argo floats, oceanic gliders) that rapidly transect the water column. Droplet microfluidics (in which nanolitre water samples are taken and subsequently operated on as droplets within an immiscible oil) is a novel microfluidic method that, in addition to other advantages, crucially offers zero Taylor dispersion and much higher analytical throughput. This project will develop the first-ever droplet-flow based field-deployable sensor for autonomous systems. Low-cost, low-powered and fully functional; the device will be a step-change in high-frequency autonomous ocean chemical analysis.
The device will exploit a novel miniature push-pull pump that can robustly sample water and disperse as uniform droplets in oil, as shown in the proposed device schematic in Fig. 1. During droplet formation, analyte-specific reagents will be added to trigger an optical response (absorbance or fluorescence) which will be quantified by a miniaturised optical detector downstream and data-logged using a microprocessor. With similar microfluidic architecture, the same pump can drive multiple flows, allowing self-calibration (e.g. by mixing reagent with a known standard), and analysis of multiple chemical species simultaneously. The device will be built on pre-existing state-of-the-art droplet-microfluidics developed by XN’s group in UoS (currently developed for human wearable healthcare devices), and microfluidic systems and field-deployment experience from AB and STV in NOC. The student will: Year-1) optimize the droplet microfluidic architecture and pumping systems to allow robust, reproducible and controllable droplet generation; Year-2) assess and implement suitable chemical assays and related optical detection technology for sensitive and accurate nutrient determination; Year-3,4) package the device into a self-sustained system, address other engineering challenges for long-term observations (e.g. device durability, battery life, etc.), and test the sensor in estuarine environments, and potentially on autonomous profiling vehicles.
The NEXUSS CDT provides state-of-the-art, highly experiential training in the application and development of cutting-edge Smart and Autonomous Observing Systems for the environmental sciences, alongside comprehensive personal and professional development. There will be extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial / government / policy partners. The student will be registered at the University of Southampton and hosted at University of Southampton’s Faculty of Engineering and the Environment. Specific training will include:
1) designing and simulation of microfluidics with CAD software and COMSOL,
2) microfabrication techniques including soft lithography, 3D printing, molding and micromilling, and microfluidics characterization with microscopes and high speed camera,
3) chemical assay design and optimization,
4) fabrication and optimization of complete sensor systems including design, assembly and integration of microfluidic, optical detection and electronic systems,
5) field deployment of sensors/analysers.
Background Reading:
Lab-on-Chip Measurement of Nitrate and Nitrite for In Situ Analysis of Natural Waters. A.D.Beaton et al., Environmental Science & Technology, 2012, 46, (17), 9548-9556.
Underwater Gliders for Ocean Research. D. L. Rudnick et al., Marine Technology Society Journal, 2004, 38, 1 48-59.
Trends in microfluidic systems for in situ chemical analysis of natural waters, A.M.Nightingale et al., Sensors & Actuators B, 2015, 221, 1398-1405.
To apply for this project, use the: apply for a NEXUSS CDT studentship